Fix: handle more key types in safejson.FromYAMLValue

[nmiyake]

Before this PR

After this PR

==COMMIT_MSG== Updates the safejson.FromYAMLValue function such that it can handle converting input maps that have any key type that can marshalled by json.Marshal (string, number, and types that implement encoding.TextMarshaler).

Previously, only handled input maps where the key type was string, which is a subset of the types that can actually be marshalled by json.Marshal. ==COMMIT_MSG==

Possible downsides?

This changes the behavior for certain inputs such that inputs that would have previously failed will now succeed. However, I believe these changes are strictly improvements/better behavior, and cannot think of a realistic case where being more supportive of input types (properly converting maps when previous calls would have returned an error) would cause issues.

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🐛 Fixes

• Updates the safejson.FromYAMLValue function such that it can handle converting input maps that have any key type that can marshalled by json.Marshal (string, number, and types that implement encoding.TextMarshaler).

  Previously, only handled input maps where the key type was string, which is a subset of the types that can actually be marshalled by json.Marshal. (#407)

[nmiyake]

Thanks! Committed your suggestions -- if you could approve again that would be great.